1. Field of the Invention
The present invention relates to an optical measuring machine having an optical system that forms on a screen an optical image of a to-be-measured object placed on a stage.
2. Description of Related Art
There has been known an optical measuring machine that irradiates illumination light to a to-be-measured object placed on a stage, magnifies and forms an optical image on a screen from light transmitted or reflected from the to-be-measured object, and measures a dimension and a profile of the to-be-measured object from the optical image magnified and formed on the screen.
In an optical measuring machine having a two-axis linear encoder on the stage, a measurement edge of the optical image of the to-be-measured object formed on the screen is matched to a reference point on the screen so as to read a two-dimensional coordinate of the stage at that time, and the dimension and the profile of the to-be-measured object is measured.
By using an edge detecting sensor provided on the screen for detecting a passage of the measurement edge of the optical image and a data processor for storing the two-dimensional coordinate of the stage when the measurement edge passes by the edge detecting sensor, the passage of the measurement edge can be automatically detected and the two-dimensional coordinate of the stage at that time can be read. Since the edge detecting sensor detects the measurement edge, the measurement data can be prevented from varying among operators depending on a sense of the operator.
There have been a variety of suggestions made from various viewpoints for the optical measuring machine having the edge detecting sensor. For instance, JP-A-3-35106 discloses that a plurality of edge detecting sensors are used in an optical measuring machine so as to shorten measurement time.
However, the optical measuring machine, in which the edge detecting sensor detects the passage of the measurement edge, may not be able to detect the measurement edge using the edge detecting sensor when the measurement edge is unclear or when a reflection measurement is performed.
Although, even in such cases, a measurement can be performed by visually matching the measurement edge of the optical image to the reference point on the screen so as to designate the measurement edge as described above, the following problem may occur.
The edge detecting sensor is generally provided at a position different from the reference point on the screen because the edge detecting sensor blocks the reference point from being visually observed when the edge detecting sensor is provided at the same position as the reference point. In this arrangement, an inconsistency may arise between visual-check measurement data and edge-detecting-sensor measurement data, the inconsistency corresponding to a distance between the reference point on the screen and the edge detecting sensor.
Accordingly, when a plurality of measurement edges are measured so as to obtain the dimension and the profile of the to-be-measured object, the whole measurement needs to be performed either by visual check or the edge detecting sensor, and it has not been possible to perform both a visual-check measurement and an edge-detecting-sensor measurement in one measurement.